Novel Reversibly Switchable Catalytic Systems and Magnetic Recyclable Nanomaterials

Currently, many smart materials as well as molecular and nano-machines employ molecular switches that can be activated by specific stimuli. In order to suit the needs in the future’s development in smart catalysis, three major characteristics in combining molecular switches and catalysts should be considered, they are: (1) ability to be switched on and off, (2) exclusive stereoselectivity and (3) recyclability. In this proposal, we intend to construct novel rotaxane-based reversibly organocatalytic systems derived from (1) mechanically interlocked molecules — [2]rotaxanes containing catalytic moieties and stations which could be activated by stimuli to control the macrocycle’s movement, and (2) hyperbranched polyrotaxanes based on the switchable [2]rotaxane-based catalytic system, in which the size (molecular dimension) of the hyperbranched molecules could be controlled by external stimuli by virtue of their reversible and collective changes in the “relax” and “contract” states for the loading of reactants and releasing products at will. The designed [2]rotaxanes could be activated by complementary switching caused by addition of acid/base and light illumination. For characterization, first, the position of the macrocycle on the [2]rotaxane during the switching processes would be characterized by standard NMR spectroscopy. Second, the intrinsic properties, the controlled switching processes and the change in molecular dimension of the hyperbranched polyrotaxanes would be characterized using NMR spectroscopy, light scattering (LS) and size exclusion chromatographic (SEC) techniques. For further applications, the [2]rotaxane-based catalytic systems would be modified and coupled with magnetic iron oxide nanospheres or other nanostructures for magnetic recycling procedures. In particular, we wish to investigate a reversible/ controllable catalytic system that can mimic the behavior of enzymes and effect organic reactions with excellent efficiency and stereoselectivity. We designed two new types of controllable catalytic systems comprised of catalyst units and controller: (A) single catalytic system; and (B) dual catalytic system. In these controllable catalytic systems, thiourea and L-proline derivative would be used as catalytic units and [2]rotaxane was used as controller. The controller could locate at or keep away from the catalytic unit depending on environmental conditions such as acid/base, light, and heat. The development of our proposed [2]rotaxane-based organocatalytic systems and their dendritic and nanoparticle materials with various modes to control the organocatalyst’s properties on demand would certainly give insights on the design of more sophisticated smart nanomaterials for future’s catalyst needs.